Okay, so in the specific scenario where:
A) Mathilde is stuck in combat,
B) and she can't teleport because she is protecting someone,
C) and she can't summon a shadowsteed,
D) and she has a teleporting fogbank spell, either as an independently developed spell or as a freebie as part of the binding process,
E) and she has enough freedom to cast the fogbank spell and summon the red rider without being ganked,
Then yes, I concede that a Red Rider performing a one man cavalry charge will probably save Mathilde's life.
A) Mathilde is stuck in combat,
B) and she can't teleport because she is protecting someone,
C) and she can't summon a shadowsteed,
D) and she has a teleporting fogbank spell, either as an independently developed spell or as a freebie as part of the binding process,
E) and she has enough freedom to cast the fogbank spell and summon the red rider without being ganked,
Then yes, I concede that a Red Rider performing a one man cavalry charge will probably save Mathilde's life.