Is she a full grown adult? If so, then depending on your location (I dunno where "Stuart" is, heh), I would guess she's a Holland Lop (US only) or Mini Lop (outside the US). Same breed, just different names depending on where you are.
Show quality Hollands have a max weight of 4 lbs but not all Holland Lops are true dwarves. Having two copies of the dwarf gene (one from each parent) results in a "peanut" - an extra tiny kit that will die at a very young age. Because of this, true dwarves only have one copy of the dwarf gene; the other chromosome has a normal version... and consequently, no matter how you go about breeding dwarf breeds, only about half the offspring will be true dwarves. The other 50%ish will be either 25% peanuts/25% false dwarves (dwarf x dwarf parents) or all false dwarves (dwarf x normal parents). Because of this, it's not uncommon for a purebred Holland Lop to be over the 4 lb mark (my Gazzles was 4.5 lbs, for example).
I think it looks more like a mini lop than a Holland lop, mainly due to the head shape and length of ears. At only 4 lbs though its on the small side so I'm wondering if it's a mini lop mixed with a smaller breed.
Definitely a Holland lop. Mini's are bigger and have longer ears and they weigh more like 6 pounds(I don't know for sure never owned one) but she is a Holland. Unless she isn't fully grown. If she is still really young yet and is still growing it could be a mini lop. Now that I look at the picture closer it kind of looks more like a Mini because Holland's faces are more smushed then a mini's. Like her face is not smushed like a hollands should be unless it was just a breeding flaw. How old did they say she was? And where did you get her from like a breeder, pet store, shelter?