The material you saw could be 'puppy matter' indicating she is pregnant as it could be that normal sticky discharge, it might be infection or crystals from her urinary tract, or if she is 58-65 days from when she was running loose it might be a sign birth should be happening soon.
Unfortunately when you let your dog run loose to free breed she could have been infected with a venereal disease such as Brucellosis which could cause her to abort her litter. You might want to get her tested for that. Herpes virus also can cause the loss of a litter as can other viral diseases.
I think a full health check up from your vet might be the best way to find out if she is pregnant and if she has any potential health issues causing litter loss or reabsorption.
Hope this helps you!
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