Of course it is your choice at the end of the day. I can only give my person opinion and that is that the cancer did not define your mother, do you really want a reminder of that part of her life?
if I were you I would concentrate more on things that gives you happy memories off your mum, or perhaps something silly that makes you think of her.
The orchid is a lovely idea, something she loved and the colours sound nice too.
Remember this doesn't have to be a rushed decision, is there anything else that makes you think of your mum, gives you fond memories etc??
I lost my mum 11yrs ago, and for the past 5/6 years have been trying to think of a tattoo that is a reminder of her and a tribute, after going from one idea to the next, it was the smallest thing that ended up being the most perfect thing. She was quite a spiritual person and she loved anything associated with native Indians, her room was filled with dream catchers, she even put some in my room and thinking about al those gave me my idea. A simple feather! To anyone else it means nothing, just a simple and pretty design (I am designing it myself and incorporating it into a pattern that will symbolizes movement/wind) to me, it makes me think of her and all those beautiful dream catchers we spent ages putting up and watching blowing in the wind, it always make me smile as it always makes me think of a happy memory with her.
I'm sorry to give you so much personal detail that you don't need to know, but so many people jump into a decision before that really think what it represents.
You will know what's right, just think of good memories with your mum and something will pop into your head and you will know to go with it.
I haven't yet had mine done, I think I have designed it to the best of my ability, I am looking for a good tattoo artist to help perfect it.
Good luck, she will be proud!