If you can, keep them next to each other for a day or two, so the new lady can get her bearings first. That takes a lot of the additional stress out of the introductions. Please stage the first meeting on neutral ground so no piggy has got home advantage or feels intruded. What your couple will have to sort out between them is the dominance aspect - which of them comes top. That can take several days or even weeks. If the sow is older and bigger than Rufio, it will be likely her who will call the shots. Most "husboars" spend the majority of their life having their advances rejected, but they are still VERY happy boys!
https://www.theguineapigforum.co.uk/threads/faq-introducing-and-reintroducing-guinea-pigs.38562/
https://www.theguineapigforum.co.uk/threads/dominance-behaviours-in-guinea-pigs.28949/
With a cross gender couple, once the initial acceptance at the beginning of the introduction has happened, fall-outs are virtually unknown.
It is normal for a sow that is not anywhere near her season (which a spayed sow will never be) to not allow any male advances, but if they like each other, this will happen in a fairly friendly, non-aggressive way. I happen to have three spayed sows, and they all get on with boars, as different as they are in personality.
https://www.theguineapigforum.co.uk/threads/faq-introducing-and-reintroducing-guinea-pigs.38562/
https://www.theguineapigforum.co.uk/threads/dominance-behaviours-in-guinea-pigs.28949/
With a cross gender couple, once the initial acceptance at the beginning of the introduction has happened, fall-outs are virtually unknown.
It is normal for a sow that is not anywhere near her season (which a spayed sow will never be) to not allow any male advances, but if they like each other, this will happen in a fairly friendly, non-aggressive way. I happen to have three spayed sows, and they all get on with boars, as different as they are in personality.