I'm by no means an expert in the field, but a lot of make up in the Victorian era contained harmful chemicals which could cause fainting. Mercury, lead, and arsenic found all be found in things from foundations to hair dyes. People did know that chemicals like arsenic were toxic if ingested, but they were still widely used in cosmetics and things like wallpaper. One of the more popular concealers was made with arsenic, chalk, and vinegar and applied to the skin to reduce the appearance of aging and blemishes. Mercuric chloride was used to lighten skin and hide freckles. White lead cosmetics were still one of the more popular methods of whitening the face, having been used by Queen Elizabeth during her reign.

However, Queen Victoria made wearing heavy cosmetics out of style during her reign. Victoria during her later life condemned heavy make up as "vulgar" and something for prostitutes, so "painted faces" largely fell out of style. People didn't stop wearing make up, they mostly just changed from a painted face (heavy, almost clownish to a modern view) to a more natural look that just highlighted a few features and concealed things like skin damage.

Women also did things like put atropa belladonna eye drops in their eyes to make them dilate, as dilated eyes were seen as attractive. This causes tachycardia, clouded vision and dizziness just by itself. The eye drops were also prescribed for people suffering from cataracts, which included Queen Victoria in her later years.

I wouldn't say it would be the only cause, but being routinely poisoned by your make up caused some fainting women. There's even records of women being killed by their make up like Maria Coventry.