It sounds like the "upside down triangle" teeth are her canines. If they are, they are supposed to be this shape.
At this age they generally tend to gring their teeth to "smooth out" high spots & interferances on the biting surfaces of their teeth. They are simply grinding them to fit into their occlusion. This can leave the teeth jagged, although I would advise against having the dentist smooth the jagged areas out, as your DD may well grind further to "correct" this. Possibly causing damage.
It may be that it settles itself when she has smoothed out the surfaces. I would be highly synical of giving a toddler a nightguard. They are forever growing & wearing such an appliance for 10-12 hrs per night would have to impede her growth. (I would have to ring my old boss to clarify) She may well just grow out of it. I have never heard of a child of this age being given a nightguard, in 15 years of Dental Experience.
I grind, oddly enough it started whilest I was working as a dental nurse at a particular practice (difficult dentist). I didn't grind before then, hence the fact that you do grow out of the childhood phase of grinding (although don't be alarmed if it does come back when her other teeth come thru, as she will have all sorts going on in her mouth at that stage & a nightguard, IMO would be a deffinite NO NO)
It should be assessed regularly, but to take active treatment as this stage would interfere with growth patterns.
However, if she is showning signs of being in discomfort, that is a different matter. I would tell you to ignore what I have said, as pain relief comes first & foremost.