My friend has a 10-year old bichon frise that started limping from one back leg about a week and a half ago.
They have examined the leg thoroughly and dog doesn't react to having any pain, but when she gets put back on the floor, she starts limping again.
The limping started when she was paying in the yard and then suddenly came back limping. There is no signs of injury or trauma.
Please advise.

Could be a back problem developing, or could be arthritis.

Have you checked the pads on the paws could be something there or they could be open

They checked her paws and there is no sign of open injury on the pads or between the toes. They hold the paw firmly (not to hurt her) and she doesn't cry or whimper in pain either
Any other suggestions?

Hmmmm... what about the nails,one could be broken

I will tell them to check on that. Thanks.!

Lrhall, if the dog is limping for more than a few days and there doesn't appear to be any physical reason for this, it is time for your friends to break open the piggy bank and take her to the vet for an examination. The reason could be something to do with the bones, joints, tendons, or as mowerman points out, she could be developing arthritis. There are medications out there that help with arthritis, bone, and joint issues. A torn tendon usually requires limiting their exercise. No running, jumping, or long walks. She needs to rest it to allow it to heal.

I will pass the information to them. Thanks.