RMB-93 is a SG. SGs have one purpose: Armor tanking. Armor combined with Flash Ammo (which reduces damage taken by a flat -3) makes all other stats (including Health) largely irrelevant for SGs. Combining this with the fact that most SG Skills are too bad to acknowledge (as they are either DPS-based or have extremely low uptime) means that the Armor stat is the only thing that matters for most SGs.

RMB-93 has slightly more base Armor than M500 and SPAS-12, which are given pre-raised at level 65 from Career Quests. RMB-93’s Skill does not have any significant impact on combat so all you would get from raising her is a slight increase in base Armor. As such, RMB-93 is still not recommended to raise.

Check the mod priority guide: https://docs.google.com/spreadsheets/d/1ty239kyJbBs1sLhTo1JvSWuN0mIJsK1nwVdI6OLLtXo/view?rm=minimal

RMB-93 sets off with one goal and one goal only: to facetank everything. Everything about her upgrade is designed to just give damage itself the middle finger.

With her new Skill 2, Pendulum Fortress, RMB-93 can stack a flat damage reduction of 4 points on herself whenever anyone in the team reloads. This caps at 3 stacks for a total of 12 points of damage reduction. Combined with Flash ammo, RMB negates up to 15 points of Damage.

Now, I’m sure some would point out “but you need to wait for dolls to reload which will take time!” and you would be right, but there is a perfect key to this problem: Defender. Defender is a 4 star SG that can be farmed from chapter 13 of the campaign and is very special because she needs to reload after EVERY shot, and a fixed reload time of 2 seconds. As you can probably surmise, Defender allows RMB-93 to quickly gain her full damage reduction with zero downtime as she’ll keep refreshing the stacks.

Now, if you don’t have Defender, then first of all please go farm for her from 13-4E immediately, but also understand that RMB-93 does lose quite a lot of her potential. Nevertheless, she still sets out to do one thing and she does that one thing very well. MOD2 is recommended for most. Her MOD3 is nice because it comes with a strong Special Equipment, but it isn’t a hard requirement. She’ll be very tanky with or without it.

Flat damage reduction is already strong to begin with, and the added HP Shields come for free if you're already bringing her other "SPEQ" along in a Doll slot. Against newer enemies, HP Shields are practically mandatory, and this just makes it so you don't need to bring another source for these. The stun is a very minor bit, as a lot of newer enemies are flat out immune to them. Overall, this is a very good upgrade for RMB-93.
Note that Dana Zane cannot proc this new HP Shield effect.