Saw the Oly 45mm f1.8 is the standard but then people say the Sigma 56mm f1.4 is just way sharper. My logic was the 45 is better for tight indoor shots at my sisters graduation next week but I want that 1.4 bokeh. Budget is $300 max so im just stuck...
Building on the earlier suggestion, I think the Olympus M.Zuiko 45mm f1.8 is just fantastic for what you need! I was so nervous about my first event but this lens is super reliable and way easier to use indoors than a longer lens. Since youre on a budget, its a total steal and leaves you some cash for extra batteries! Quick tip: stay around f2.0 or f2.2 if you want to make sure her whole face stays sharp while still getting that lovely bokeh. Also, check out the Panasonic Lumix G 42.5mm f1.7 ASPH Power OIS as an alternative because the built-in stabilization is amazing for shaky beginner hands like mine! Youre gonna get such great shots!
To add to the point above, definitely be careful with focal length indoors... you might run out of room to back up in a crowd. I would suggest the Sigma 30mm f1.4 DC DN Contemporary since it hits that f1.4 requirement while usually staying under $300.
Unfortunately, some of those smaller primes just arent as good as expected when the lighting gets tricky. I had issues with one of mine failing right before a shoot once. Just go with Sigma, honestly. You cant go wrong with their primes for portraits. They feel way more solid than the plastic stuff and the rendering is much better anyway.