The short answer is yes. The long answer is: it's a bit more complicated.

The IRA as an organization wasn't a monolith, existing in several different forms since 1917. The IRA - at least when they had the operational security to do so - would officially swear in members, who'd become known as "Volunteers", probably in reference to the Irish Volunteers of 1917. Women were often prevented from becoming "volunteers" during the early years of the conflict (I know you're asking about the 1990s and Im assuming by extension the Troubles, but context is important), though this changed pretty dramatically during The Troubles of 1969-1998.

Some important caveats: even if women weren't necessarily Volunteers, they still often had important roles. In Derry, Northern Ireland, there are murals dedicated to the women who would bang trash can lids/pans against the pavement during British/RUC raids in the Bogside. Women also used their homes to house weapons and materials.

Now, to address the meat of your question: yes, there were women Volunteers in the Provisional Irish Republican Army. One of the most famous was Dolours Price, who was allegedly involved with a prominent IRA Brigade in West Belfast, along with her sister Marian. Both were recognized Volunteers and participated in IRA operations. In 1973, she - along with her sister and several others - bombed the Old Bailey in London and was found guilty at trial of the event. Both were imprisoned and participated in their own hunger strikes which lasted over 200 days because they were force fed, which caused a pretty international scandal at the time.

So clearly women could be active members of the IRA during the period. But the Troubles are seriously messy, with so many splits and competing organizations claiming to uphold the true tenets of Irish Republicanism. I have read texts that by their demise in the mid 1970s, women could be sworn in to the Official IRA, but I've also seen contradictory information to the contrary: as a nominally Marxist group, it would make ideological sense to allow this, but everyone knows that's not how the world often operates.

Now, we also have to discuss the relationship of political parties to their military arms. Maybe the most famous woman from the Troubles, Bernadette Devlin (a former People's Democracy student movement organizer and present at Bloody Sunday) served on the Executive of the Irish Republican Socialist Party during its early years; this party was related to the Irish National Liberation Army, a violent armed group. Interestingly, Bernadette left the IRSP because the rest of the Executive refused to rein in the INLA and place them under their direct auspices.

Sinn Fein is even trickier. Sinn Fein's role during the 1970s and through the 1980s changes WILDLY. It was often seen as a "rubber stamp" group that simply passed off political positions expedient to the PIRA's goals. This changes a bit as Gerry Adams rises in political prominence, though there was of course talk that these changes meant even MORE complicity with the IRA, as no one could agree on Adam's continued participation with the Army Council. His... I guess we can essentially call him PR man?... Danny Morrison once stated that Sinn Fein through the Peace Process in the 1990s was predominately "men beyond military age and women". So while these women would not be "Volunteers", it is entirely possible - and honestly likely - that they did not have control over military operations or policy, they would have been directly associated with the movement.

For source reading, I'd suggest the following:

The Lost Revolution: The History of the Official IRA by Hanley & Millar (2009)

One Man's Terrorist: A Political History of the IRA by Daniel Finn (2019)

Say Nothing: A True Story of Murder and Memory in Northern Ireland by Patrick Radden Keefe (2018/2019)

TL;DR - Yes women could and would be members of the IRA (depending on which faction you mean) into the 90's.

In the midst of splinter groups and political upheaval, questions such as these tend to get a little murky. To start:

The Irish Republican Army (1914)

For women interested in the fight for unification or otherwise Irish Republicanism, Cumann na mBan has been around since the 2nd of April 1914 and celebrated it's centennial 6 years ago. Cumann na mBan members participated in both armed activities alongside IRA men (see: Winnie Carney) as well as hospital and ration duties.

Getting to the 90's

There was also a brief history with the Provos and Cumann na mBan pushing past the internal split in the IRA around 69/70. This divided the organization somewhat in half, splitting those who wanted to continue the insurrection and those who wanted to push more politically. Cumann na mBan also was involved in these changes and for a short time was grouped with the Provo's

"The spell of Cumann na mBan within the Provisionals was short-lived anyways. In 1986, they parted ways and Cumann na mBan issued a statement in support of those who staged a walk-out in support of abstentionism at the Sinn Féin Ard-Fheis. A number of mainly Northern women who had family links with the Provisionals left but the small Cumann na mBan organisation remained intact.

The Provisionals had already prepared for the break-up of Cumann na mBan by recruiting women into the IRA and setting up of a Sinn Féin Women’s Department in the early 1980s. Thus, there were no attempts to set up an opposing Provisional Cumann na mBan group. Instead, they claim that the women’s organisation ceased to exist in the 1970s. That is clearly a case of re-writing history, considering the fact that the British Government still list it as a terrorist organisation.

With the 1986 split, Cumann na mBan had cut its roots with the Provisional Republican Movement. Thus, none of the more recent splits such as 32CSC/32CSM, éirígí, or the Real IRA set up their own versions of Cumann na mBan; also the newer organisation such as RNU, the 1916 Societies, ONH, or New IRA made no attempts yet either. In essence, while the name Sinn Féin is contested, besides there is a RSF-affiliated Fianna Éireann group and both 32CSM and RNU made in the past various attempts to set up their own Fianna groups, and there is a mingle-mangle of groups and individuals using the term “IRA,” there is only one Cumann na mBan. One might argue that groups and individuals had split from this organisation in the past 102 years but, ultimately, there was always only one Cumann na mBan and this is still the same women’s organisation as the group founded in April 1914."
(https://me.eui.eu/dieter-reinisch/blog/cnamb/)

​

The article below from 1996 specifies 5 men and a woman convictedhttps://www.irishtimes.com/news/six-jailed-for-arms-crimes-salute-as-supports-shout-up-the-republic-1.23743

Also, the British Gov still had them listed on their list of terrorists even up to the Terrorism Act of 2000 legislation.gov.uk/ukpga/2000/11/schedule/2