And please do not bash or critize me because I know what happened, shouldnt have..

but I need sound advice.
I have a terrier/cocker mix female turned a year in november that weighs 10 pounds. We brought her into my house because she was being neglected when she was just a few weeks old.
In august we got a free cocker spainel pup for my son for his 10th birthday. He is approx. 9 months old, 16 pounds.
Nahla, the female went into heat we "thought" at the end of Jan. First dog for us to go into heat, dont know much about it. NO INTENTIONS what so ever of breeding. Low on funds, we were waiting on our incime tax money to come back to get them both fixed.
When we noticed she was bleeding, we kept the two of them apart. Like seperate rooms, in kennels, not anywhere near each other apart.
This past week we have noticed that her nipples were enlarged. I had to take her to the vets for her pre spay ck up and a ear infection so I asked the vet
While we were there what she thought. Xrays were done, from what was seen she is pregnant, with just one that they coukd see.

.
They only thing that I could think is how it happened if she was in heat before we actuallly knew and when my kids put them outside in the fence yard after school they connected. Other than that I have no clue how. :/
This poses several issues as most of the breeders know.
Most small dogs carrying singeltons need c sections, because pup is either too big or they dont go into labor on their own. Its not even gaurented that if a c section was done the pup will survive. Because she was able to see the pup she is far enough along and is about 10 to 15 days of giving birth.
So the options we were giving were.. Abort/spay. Schedule a csection that will not guarantee us a heathly mom/pup for 800 plus dollars that we cannot afford or let her try and have it hoping she does well which also doesnt guarentee a healthy mom/pup or she could need an emergency csection costing us even more money.. She did say we could wait as long as possible to spay her to see if the pup will survive still calling it a spay/abort (cheaper) but most of the time the pup is born to premature and will die.
So even no my heart is breaking and I feel so bad that this even happened we have chosen to spay/abort and she is going on Monday.
Please, please tell me Im doing the right thing..