
to be honest you won't even be able to guess until she is grown up, as most puppies of any breed can look similar.
You need to look at the probabilities of what dogs are likely to be running loose in country areas, the most likely culprits are as you say, terriers, border collies or spaniel or retriever, unless there was a specific other who fits the bill.
If from a city area most of the crosses around here for example are going to be Staffie crosses, with the rest, collie or various other terrier crosses.
Barbara and the Grey Curly Tails.