Thanks for using the forum.
A small amount of bruising at the injection site is not uncommon. Your mother can speak with her doctor about needle size and her concerns. If she is on any kind of blood thinning medication she is more likely to have bruising. Make sure she is not injecting in the same spot every time. Without seeing the bruising, it is not possible for me to determine if there is any cause for concern. For that reason I would recommend that your mother speak with her MD when she can.
bruising does happen, for most of us its not very often. she may need shorter smaller needles they come 5mm (1/4inch) and 30 or 32 gauge. She may want to show the MD her bruises. Is she on a blood thinner? My MD looked at my bruises and said not to worry I dont know about Her bruises though.