Well, if the candle go down to the bottom of the glass and got hotter than 100F the pla could sag and the candle could slide off and burn down the house.
Take a look at what is sold, you won't find many plastic candle holders.. I did have so tee lites that were in plastic of some kind .. PETG or ABS would be better but they all burn and melt.. Sort of like using wood .. you wouldn't do that ..

PLA can be thermoformed in hot water, goggle the term.. place pla in boiling water it becomes like limp pasta till it cools again