One of the basic rules I TRY to teach my kids is that "if it's not yours, you keep your hands off of it." This is a basic rule for KIDS. SIL, as an adult, should have this down pat. Emphasis on SHOULD.
I fear, OP, that if you say anything to SIL, she's going to go with the "I was only trying to HEEELLLLLLPPPPP" line (whine) and go all dramatic martyr on you, like YOU are wronging HER for daring to be mad at what she did. And at that point, you just have to thicken up that skin and say icily, "I never asked for your help. I never wanted your help. And the fact is that you DIDN'T help. You didn't know anything about the area in which you tried to 'help', and you destroyed something precious to me. You just didn't CARE."
And if she says she 'didn't know' how precious they were (as if that absolves her), you can always go back to the fact of, "but you didn't ask. You didn't CARE to ask or make sure that you knew what you were doing. You just came in and destroyed my belongings. And do you realize how thoroughly ridiculous that sounds as an excuse? What do you expect me to do....go through each and every item in my home and tell you how important it is to me, just so you don't destroy anything else? Sheesh!"
And I would CERTAINLY ask her to reimburse you for the plants. Tell her that if she's really sorry, there shouldn't be any issue with this. And even if she's not sorry, she still has the obligation to reimburse you. (And if you want to go one better, tell her that you'll be hiring professional landscapers to undo her mess, and she'll be the one receiving the bill. Either that, or she can buy you new plants and buy the plane tickets for your mom to visit you and replant the plants. Personally, I think you should throw this little nugget out there. Make her sweat it. Make it hurt for her. She needs to be uncomfortable, and THAT is the only thing that will make an impression.)