As a limited answer, addressing just your questions:
- if she's Human, she could pick up one of the many Initiative-improving Talents via versatility
- if she's wearing armor with an initiative penalty, she could swap out with an alternative that has no penalty or with a Thread Item whose ranks eventually reduce or eliminate the penalty
- if you allow casters to use shields in your ED, same as above but for the shield
- one of the approved Rank effects for Thread Items in ED4 is bonus to Initiatve test
- when she hits Circle 5, she could consider multi-Discipline into a Discipline with some Initiatve engaging traits and/or talents
To address the heart of the matter:
Casters aren't meant to be fast. They are likely faster than folks who wear stacks of heavy armor and shields, but they have no inherent ability to improve Initiative above their DEX step (caveat: I think there's a spell that can be brought to bear). And that should be okay - no one should be good at everything.
If you increase her speed, the fighty guys are likely to inevitably ask "why is the caster going before me" or, minimally, "why is the caster going as fast as me?" Probably won't happen with a small bump, but likely will with a large bump, especially if the fighty guys are using Talents to improve their Initiative. Furthermore, your post suggests that she has a significant deficit in Initiative (if she's "always going last"). Good chance that trying to "fix" that could lead to jealous or later balance problems as other players say "hey, she has an item that gives like +5 to her Initiative Step, why can't I get something that gives me +5 to (insert warping statistic here, you have plenty to choose from)."
You may be better off extolling the virtues of going last - and there are virtues to it, it's not 100% minuses.
Random extra note: probably better to have a GM related question in the GM forum.
Some would consider Rank effects for Thread Items spoil-territory (it is in the GMG, after all). Not chiding, just a suggestion.