Regardless of how old Glenn is in the show, I'm sort of under the opinion that outburst had nothing to do with Betty wanting to protect Sally from Glenn. Just like the running theme of Betty's narcissistic, almost referential maniac (to use a made up affliction) state of mind that manifests every time she speaks about the kids, especially in the psychologist's office, I think she is making this totally about herself. Betty has connected with Glenn on a couple different occasions, and got called out big time by Glenn's Mom for giving him a lock of her hair(???). Regardless of whatever else Betty is, I think you can definitely say she is a fucking child. I think she sees Sally with Glenn, someone that she had connected with (which was enforced by her screaming, "You don't know him!!" er whatever the fuck she said), and in some weird fucky kind of super reverse Oedipal mode, is almost jealous. Or maybe we don't have to go that far. Maybe we can say that Betty has negative feelings towards Glenn, because the strangeness and inappropriateness of what she did in giving him the hair, and being called out on it. Maybe she feels resentful because Glenn's mother that called her out was a divorcee, something Betty gossiped about with the friend of Betty's that disappeared, and Betty's family was ruined in a likely similar way and now she is stuck with Francis when she still feels the burn deep in her loins for Don. Or maybe Betty just feels a sense of embarrassment when she sees Glenn and doesn't want Sally around him. No matter what, that wasn't motivated by Good Parenting in my opinion. If anyone has read Pope's The Rape of the Lock, I think you can definitely see some of what the director was doing in having Betty so freely give him her hair and all he had to do was ask (yes, I think that scene was influenced by the poem)... But I don't want to go into all that.