So I'm trying to find an alien invasion type movie that probably came out in the late 90s. The aliens were worm-like. The characters think they've won but then at the end you see one of the worm-things move across a woman's forehead while she's taking a bath. I know this is super vague. A friend and I just watched Annihilation (Natalie Portman) and she said the plot reminded her of this worm-movie.
This sounds like a misremembered combination of Shivers (1975), and Night Of The Creeps (1986). Both have horrible wormy slug-parasites which go into people, just like Slither (2006).
In Shivers, there is an infestation of worms or slugs which spread from host to host, mostly via sex, and control the bodies of their hosts. There's a scene with a worm and a woman in the bath as you describe.
However that film definitely does not end with the characters thinking they've won. Instead everyone in the apartment building gets worms in them, or killed, and infected people stream out of the neighbourhood to infect the rest of the world.
In Night Of The Creeps there's the same worm possession/infection thing going on, but no bath scene. However at the end the main characters think they've won, (as your comment says) but they don't realise there are some other alien worms not dead, and creeping away to start infecting the bodies in the graveyard.
So I suggest your friend has seen both, and combined them in her memory. It would be very easy to do, as the films are thematically so similar.