What just happened

So we have decided to foster a family members child and she has no clue how to do anything she is 17 and mentally disabled just a little so today she said she was unsure if she was pregnant and I went and got her two test well first one was neg so I keep the second one now I tested with opk all month never ovulated and just for fun I took the second one that came out so dark almost no control line I am like floored we had just decided it was not the right time with our new addition and I was worried she was pregnant then bam I am and have no clue.