To begin, it's important to be a bit more specific about the groups mentioned in the question - leftists and feminists. 'Leftist' was a term used somewhat in this period, but not nearly as widely as labels like "social democrat", "socialist", or "communist". So although it's not strictly speaking an anachronistic term, it's not very precise in this context as there were many different strands of left-wing thought and activism at this time. Likewise, plenty of people called themselves 'feminists' at this time, but this too was a diverse collection of people and viewpoints.

So a literal answer to the 'what did they think about Thatcher in 1979' would be that they thought a lot of different contradictory things. But we can unpack things a bit further and make some general contextual points:

- UK in crisis - Thatcher's election and premiership is best understood in the context of the prolonged and severe economic crises of the 1970s. Serious union disputes, out of control inflation, complex unresolved problems with the European Common Market, Rhodesia, Northern Ireland and so on. The point being, Thatcher's election in 1979 was above all a response to this situation, and her radical shaking-up of decades of consensus was the primary lens through which she was seen, both then and now.

- Thatcher as a non or anti-feminist - famously, Thatcher herself resisted portraying herself as an 'female politician' (the first volume of Charles Moore's biography is very good on this), and was hostile to either a policy agenda focussed on 'women's issues' or more symbolic approaches towards female empowerment (e.g. the gender balance of her cabinet).

- Thatcher as relatively little-known in 1979 - seeing as the question specifically asks about how she was viewed in 1979, it is worth remembering that the public perception of Thatcher was far less well defined then than it would become a decade later. Her win in the '75 leadership contest was a major surprise for a relatively obscure politician, and much attention was on struggles with in the Labour government, and between the government and the trade unions.

In short, in 1979 although Thatcher's sex made her notable and unique, she was primarily understood not in gendered terms - partly because she resisted such a framing herself - but as offering a dramatic break with the post-war economic consensus, and a potential solution to a decade of malaise. What "leftists and feminists" thought of her varied, but had more to do with her approach to foreign policy and, especially, economics than her gender.

Edit: typos