I believe that for registration purposes, if the parents were minis, then the puppies are minis, and likewise for toys. You can have multiple types in the pedigree, however, which makes it challenging to say sometimes. She looks and sounds like a toy to me (my slightly oversized toy is 8 pounds and just barely over the height restriction for toys at the withers, so she would be right in the range expected for a toy), and here is a link to Poodle growth charts. POODLE PUPPY GROWTH CHARTS
Poodles are just registered as poodles, not as standard/miniature/toy poodles. I think that if your 4 1/2 month old puppy weighs 5 pounds it is going to remain a toy poodle. Are both its parents toys? Knowing their size will help you know how big your puppy is likely to grow.
A dog is a toy if both parents are toys, same for minis. When a toy is bred with a mini (which shouldn’t happen ideally), then I guess you can call it whatever you want... A big toy is called an oversized toy, a big mini an oversized mini.
If you see a toy next to a miniature, it’s really easy to tell them apart. A toy has very delicate bones and features compared to a mini. An oversized toy, the size of a mini, will be taller but still look delicate. Minis look like small standards. Toys look like a more fragile version of them.