Trimming roots

[Big Bubble00]

So I have an Amazon Sword that has lots of very long roots and sometimes some of them went out of the substrate. So here are some questions:
1) Can I trim my Amazon Sword's roots? If I do, will I hurt it?
2) I adviced my sister to buy a new tank and some real plants for her betta fish because fake plants don't give anything beneficial for her betta and might upset the betta. My sister also have some colourful pebbles as her subtrate in her tank, will it harm the plants that she is going to buy? (I advised her to buy egeria densa since they are easier to grow and take care)

 

[Delapool]

I've trimmed roots before (also for the garden) and always thought plants don't like it (along with being shifted) but generally will bounce back. A couple of root tab ferts may help.

On the gravel as long as listed as aquarium safe, I would think ok.