Moms work hard to ensure that their kids have everything they need. Even if you are an adult, you want to reward your mom for all the hard work she did when you were young. A birthday is an occasion when you can spoil your mom and work hard for her. If nothing else, it can be a day where your mom doesn't have to work too hard.
If you think your mom deserves some time to relax and unwind, then getting a spa day for her is a way to do this. If you are well off, you can make it into a spa weekend, where your mom will stay overnight in a resort and be pampered. Spa days usually involve aromatherapy, massages and beauty treatments. If your mom likes these sorts of things a spa day will be a good gift for her.
Being a mother is intrinsically linked with the idea of birth. If your mother likes jewelry, then buying her a birthstone is a personal and lasting gift. Look up your mother's birthstone, based on her month of birth, and buy her one of these. There are a variety of birthstones for each month, meaning that even if you don't have the budget for a diamond if your Mom was born in April, you can buy her quartz jewelry.
Breakfast in Bed
If you still live at home, and you think your mom deserves a lie-in, make her breakfast in bed. Tell her the night before that this is what you are planning so she will stay in bed in the morning. Buy a luxury breakfast, with pastries and fresh fruit. Buy something that your mom doesn't usually have for breakfast so that she will enjoy the birthday treat. You can give her a birthday card with her breakfast.
If you do not have a lot of money, then search through your old photos for a picture of yourself and your siblings that you think your mom will enjoy. Make a photo frame, if you are skilled with wood or other materials, or buy one from a store. Put the picture in the frame and wrap it. This is a cheap but effective gift, since your mom will be able to put it on her desk and be constantly reminded of you.