Small lump on ten week old chihuahuas belly?

most likely an umbilical hernia.

it can be repaired when she is spayed.

point it out to the vet when she is there for her next shots. The vet can confirm what it is.

It is possibly an umbilical hernia. Without treatment it could cause problems, however when she is spayed the vet will include it's removal without any additional cost.

Beware, vets are now advising that our females should have reached their full growth before they are spayed. Unfortunately I don't know how this impacts on an umbilical hernia. Talk to vets who you trust or Google this.

Where about is this lump could be a Umbilical hernia .

I belive that not a good sign you should take.her to the vet to get some.answers of what it might be asap