What can I give my mom to eat that will give her more stamina and energy?

I agree with the idea of an evaluation. I'd be making her well blended smoothies with Greek yogurt (more protein than regular yogurt), milk of some kind, added protein powder, some fruit (blueberries or mango or banana), and some ground flaxseed to help with her bowels. You could also add a bit of light olive oil for calories and fat. Or peanut or almond butter. Or ice cream instead of the milk.

Jello is very low in calories and nutrition. I get my mom little jello "cheesecake things" that are strawberry or raspberry flavor, but still not much nutrition or calories. I also give her tapioca or rice pudding. If you have time, I'd make it yourself and add dry milk or protein powder for more substance.

Ask Hospice to do an evaluation, they can determine if she needs a visiting nurse. Lack of appetite and loss of mobility are serious indications of end stages. You may see her sleeping more, and she may need comfort medications, all part of the evaluation.