My female puppy has a pimple-like lump on her private area. What is it?

Hi there and thank you for using pet coach to address your concern. From the picture you provided and knowing that Lucy is a young dog, this is likely nothing to be concerned about. It appears as though this may be a pustule and that she may have a bit of a skin infection in that area. This can commonly occur in females that have extra skin folds around the vulva which it does appear that Lucy does have some excess skin around the area where urine could potentially become trapped. I would recommend using a topical medication called zymox topical ointment. If this bump is from a skin infection then I would expect it to resolve in about 7 to 14 days with topical treatment. Once this resolves, I would recommend keeping her private area clean using malacetic conditioning spray. If more bumps begin to show up or this bump persists or worsens then I would recommend having a veterinarian take a look at this for further testing and treatment recommendations. Lucy may need to be put on an oral antibiotic in addition to topical therapy to treat this. I hope this helps! Please feel free to contact me with any other questions or concerns that you may have. I am also available via consultation if needed.