Hi Daniella
It's so good that you and your sister are going to visit your Mom in April I do hope that you all have a wonderful time together.
I am not a mom so know little about mother daughter relationships, to offer advice. I think it's important to understand that your mom may not be as physically strong as you remember her because of the surgery and the cancer, both of these things can make a person feel tired very easily, this may not be the case with your mom, but it may be worth keeping in mind when you visit.
I am sure she will be overjoyed to see you. You could take her photos of yourself in a pretty frame that she can keep with her, write her a poem, paint her a picture, express your feelings for her and how happy you are to be seeing her. Take a camera. Perhaps you could make a video of your visit, make copies so you will all have one.
Most important, be yourself, enjoy and make happy memories.
If you were my daughter I would be very proud of you and the mature way you are dealing with your moms illness, it takes a lot of guts to come on here and ask for help.
God bless you
Cee