Cause it will probably hurt her ass. It wasn't made to go in her ass so it shouldn't be put in her ass. Just use basic lube, save the tingling stuff for her pussy.
I haven't had anal, but I would say just go slow take it easy. If it doesn't go maybe try it another night. Don't be discouraged, by it not going in at first.
What is it you want to hear ? Is she up for it ? Geeez do you want somebody else to do it for you ? thers is no set of rules and list of toys for it. Everybody is different get it ?
Has she done it before. If she has it should be easy. If she has not then it's going to hurt her like a motherfucker. My advice is to start slow. build up to anal. She needs to be totally comfortable with being exposed like that. If you touch her asshole and it clenched up then she is not ready. Start by using a finger and progress to maybe 2 finger. It may take days or weeks for her to be comfortable enough to relax the sphincter. once she finally is then you can actually have anal sex. Lots of lube and go slow cause the first time really does hurt.
then try it. Just work your way up to it. Use foreplay. She must be relaxed and really willing to try or it will go badly. Use your fingers at first and yes lube lube. Go slowly take your time. She's either gonna be into or not. there is no science to it. Peace