it's ok to poop once a day; and tha't s great that she's going by herself on the pee pad. if she's not eating much then she won't poop much; my dog eats 3 times daily and she poops once in the morning and once at night; so that's normal
you can try giving her a piece of lettuce, baby carot or litle piece of apple without the skin; they usually like that and it might open her appetite.
you and your puppy are doing great; keep up the good work.
