Showable holland Lops have one dwarf gene, this makes them smaller, their ears shorter and gives a bulldog face, breeders also like them to have a 'skirt' which is extra flabby skin on their butts.
BUT you also get Hollands in a litter that didnt get the dwarf gene and are larger. They tend to have a 'camel' face and still have a skirt which is not caused by the dwarf gene.
Mini lops tend to have a naturally pudgy face, not nearly as extreme as the show holland, and a very meaty frame. They should be round all over when posed and look like a basketball when looking down on them and half a basket ball when viewed from the side.
These are show quality traits and, at least around here, lops are often crossed with each other since pedigrees and rabbit showing is not a big thing but small lop eared rabbits are! I have pedigreed mini lops but also small lop mutts that I cross with my purebreds.
You can use a scale that fishermen use or place her in an enclosed box and weigh that then weigh just the box and subtract it. But you cannot tell by weight alone which breed she is.
Your pictures are not really clear enough to tell what Marshmellow is for sure but from the shape of her head and the extra skin around her hips I am leaning toward Holland but she definately lacks to dwarf gene as her ears are too long.