Because of course a foreign title is going to hold weight with American politicians

I mean points for her taking action, but come on.
As for "laying low," I don't buy it. A big agency like that doesn't take on a new client (and announce it publicly) to lay low. Might be part of a long term strategy in the years to come, but in this case they needed some early wins to not only establish Meghan as a sought-after personality/brand, but to make some money for themselves. (It's possible she's paying them a retainer, but AFAIK agencies like that work off commissions - big ones.)
There's so much noise out there about both of them, in part due to their actions (ie the lawsuits), and a lot that they can't control. Way too many so-called experts offering their opinions and anonymous sources saying whatever they want, so that it's a sea of noise with little of it based on fact, but highly effective in influencing public opinion just out of sheer volume.
What Meghan needs now are some wins - a brand contract or two, something with enough profile to lead the way for others to want to work with her, lots of pictures (red carpet events or staged outings that showcase her style and her legitimacy as a celebrity), perhaps a regular column in a major lifestyle media outlet (ie Vogue), and some serious charity work beyond writing letters - for example signing on as an ambassador or patron of a known charity, hosting a high profile charity event, perhaps hosting or voicing an important documentary. To cut through the noise and establish/grow her brand, overcome the damage Harry's done and rehabilitate their reputation as a couple, she needs all of these things combined IMO.