You couldn't persuade her to cycle fishless? Then she could have (almost) what she wants afterwards.
(Anyway, how can you get more colour than with livebearers? I've got a silvertailed female guppy, a yellow/black-tailed d
, a male with large red tail, also a red platy with black fins, a black platy with bright yellow edges and a totally goofy-looking pink Mickey Mouse-platy all in the same tank; any more colour than that and we would have to issue sunglasses to visitors.
I am technically understocked at the moment, but there is life everywhere I look in that tank, they are so active.)
However, guppies are no longer considered suitable cycling fish, I've heard, due to not being as hardy as they were. That was one reason for my going fishless, that my daughter really wanted them.
If your mum wants something a bit more challenging than livebearers, then water stats are going to be more important - which suggests that fishless may be the way forward. Can't you twist her arm?