The most likely scenario is that Queen Victoria's being a carrier resulted from a genetic mutation. Apparently, about a third of haemophilia cases appear in families with no previous history, so mutations are not all that uncommon.
There has been a suggestion - discussed elsewhere on the Forum - that Queen Victoria was not fathered by the Duke of Kent, but by an unknown haemophiliac. This was first postulated by writers who believed - erroneously - that there was no porphyria among Victoria's descendants, but there was haemophilia. However, if you read Purple Secret by John Rohl et al, it is clear that there was quite a lot of porphyria among Victoria's descendants.
It is also unlikely in any event that a haemophiliac could have fathered Queen Victoria for a number of reasons. First, and most obviously, it is unlikely in those days that a haemophiliac would have lived long enough and in sufficiently good health to father children (the only royal haemophiliac who did was Leopold of Albany). Second, there is no evidence whatever that Victoria's mother had an affair during her husband's lifetime (there were rumours involving her comptroller, Sir John Conroy, but these involve her during her widowhood).
It does seem that the haemophilia gene has now been bred out of the royal families of Europe. As far as I know, the last living royal haemophiliacs were the two haemophiliac sons of Alfonso XIII of Spain, who both died in the 1930s, and Waldemar of Prussia, son of Heinrich of Prussia and Irene of Hesse, who died in 1945.
Hope that answers your questions.
Ann