Look for a recumbent tadpole trike, it is easy to ride, very comfortable and stable. Upright trikes are not super stable and easy to get on two wheels if not careful.

Icetrike, CatTrike, HP Velotechnik, Terra Trike are all good options and you might even look at something with electric assist to help her out.

If she was going that slow that is bad and that is the easiest time to be unstable. You might have her join up with an adult learning class. Keep in mind I meant that seriously and not as a joke or an insult, learning to ride a bicycle as an adult is harder and if you aren't sure of yourself having a good course of fellow adults going through the process is helpful even if you know how to do it relearning in a less stressful open environment can make a big difference, seeing other people in a similar position takes the stress and scare out of it. If you feel like you are the only one it is frustrating and sometimes humiliating so other people around who also have those feelings makes it more fun and less challenging.

It can also be quite hard to get back on after a big crash like that. I know I am a little skittish a little in certain conditions after some crashes but you power through things and you get back to normal.