She doesn't need a bodyguard. She have near absolute defense AND offense. She's effectively one of strongest parahuman out there.
Also Legend power isn't suited for bodyguard job. He have good offense (he's pratically an artillery), excellent movement and good personal defense (breaker state), but he have nothing to protect others.
Legend's def is more decent what it does is change him into the form when hit and use a portion of the impact energy to heal him then continue for the rest which is pretty good for normal fights especially with the evasion his flight offers basically making him immune to death by 1000 cuts but a single decent hit will have him useless in his breaker form for a while.
Everyone going "But Joe doesn't know about <Character>, how can he know they're not important?"
But, Joe doesn't need to know about them. He just needs to wonder "Are there more than 4 parahumans necessary?", and feel for the big smug "nope" sensation from his Passenger. Heck, he knows that Flechette and Taylor are important, and he might know that Amy is, but… he may not know who the fourth is. Just that there is a fourth, and that one of the four (who is not Taylor or Flechette) is currently optional.
(Especially since… the only reason they were able to get everyone together and rallied to fight Zion was because he went on a murder-spree. Which might mean that number four is Jack… PTV saying he's "important" for stopping Zion is one of the main reason that Cauldron let him continue as he is, after all.)
He knows that number 4 is Riley/Bonesaw as has already been covered it's been said in the story that he knew that and decided to off her anyway cause he's confident he can fulfil whatever her role is since he thinks it's a biotinker thing which as also already covered it isn't but he's already fulfilled her actual role anyway.
Both have shown competence to a degree with Scrub when coming out of the drugged haze having serious second thoughts especially when he thought he killed Kephri but Skidmark worked to keep him in a drugged haze which is now cleared up. Armsy had the less so with his canon stuff followed by playing political games by spreading the transcript to make Piggot look bad (and it really will be now it's clear contact with Apeiron is positive and results in free power ups but she salted the ground for it) and going to face Lung with Weld while concussed which can really be written off as being concussed.
However, since then he's recognised the situation and where it's headed, distanced himself from the blame by staying as far from the action as possible, recovered, gained pr points from the fake clean up and even been the first outside the forge to crack basic dust weaving via copying Garment's designs.