My twos cents are:
Penny #1: The whole high-pressure/FB 'attack' thing was out of line but
Penny #2: Most good b*r*e*e*d*e*r*s do maintain
some form of contact with their buyers.
As a dog buyer (or buyer of anything for that matter) it is prudent to maintain a civil rel
ationship with whoever you purchased it from in the event that there are any problems. Purebreds quite often have particular genetic health issues and all responsible sellers have a policy re: liability / health guarantee / replacement dogs.
When my cavlier had to have knee surgery, even though it was past the date listed in our agreement, the seller told me she would give me another dog - I didn't take her up on her offer but she was good to offer and she might not have if I had been unfriendly during our negotiations.
My friend has owned Afghan hounds for years and built up a very valuable rel
ationship with 'her' b*r*e*e*d*e*r* and their network. This enabled her to get good prices, good referrals to vet resources, and wonderful support (and replacement animals) when two of her dogs died from unforseen medical conditions. Her dog seller (*gah* idk why the b-word has to be moderated!

) is on FB w/ my friend (they play FV together lol

). They are more business 'acquaintances' (incidentally a new category on FB

) than friend-friends, but it has been in my friend's interest to foster the rel
ationship.
People usually ask for an email address these days during business transactions, or businesses will say "check out our website/check us out on FB", but the idea of "You bought X from me and now we're FB friends" seems really inappropriate and frankly unprofessional to me.
As long as you have nothing to lose by having her as a potential SS enemy, I would not waste any time worrying about letting her be your "Friend."