Hello. =) There are a good few threads on anal hanging about already so the search function may be a good place to look just to get the full depth of info.
First thing I would suggest is to dump using the improvised opjects if you haven't already and invest in some good safe toys. It's a lot better for your health, trust me. =)
Numbing lubes really aren't a good idea. Pain is a sign that something is irritating or potentially dangerous and masking the pain doesn't get rid of that irritation. In fact, it can potentially lead to you or your partner not realizing when something has gone too far and be even more dangerous. The back passage is a very delicate place and it can be extremely easy for it to be torn if you are too rough. It's perfectly possible to have healthy, safe and fun anal sex, after all people on here have been going it themselves for years, but one of the ways of being safe is to listen to your body. Pain is one of the things you need to listen for.
If you are given enough time to relax and enter without causing any discomfort then you are probably relaxed enough. Any after pain could be caused by a good many things and it may be a good idea for her to get checked out by a gp or health care provider just to make sure she doesn't have any sort of issue with her digestive system if she is getting consistant pain.
Personally, to me it seems as if you are maybe being a bit too rough and not using enough good quality, thick lube suitable for anal play. When you are going at it, it can be very easy to discomfort to be masked by the enjoyment of the act and it isn't untill you begin to come down you notice the ouchies.
For anal, you really should be nearly drentched in lube to be really comfortable. If you are worried about mess then it may be good to put a towel down or somesuch. Any time you feel like you may be drying, reactivate with a bit of water if it's water based or reapply more lube.
Perhaps you could try having very gentle, slow, relaxed anal next time just to see if the pain may be caused by rough thrusting or there is something with her bowel that resents being disturbed?