Worth separating two different problems here: capturing the missed call, and what happens to that person after.
A trades business I support had this exact issue, can't take inbound calls while driving or mid-job, voicemail piles up, and anyone who doesn't leave a message is just gone. The fix wasn't an auto-text. The outbound voicemail gives callers a form on the website instead, same intake questions admin would ask live, mostly multiple choice with room for detail. Submissions land in a sheet, so by the time admin calls back, they already have the caller's actual situation in hand, not just a name and number.
That callback still matters, maybe more than people think. When it's someone's home on the line, the admin conversation isn't just order-taking, it's where the sale actually closes. A text can acknowledge someone. It can't build the trust that gets a homeowner comfortable handing over their house to your crew. That part still needs a real conversation.
So before setting up a pure auto-text, worth asking what you actually want it to do beyond acknowledging the message. Your admin is clearly good at the sales side when she's free, the question is whether whatever catches the overflow sets her up to pick that conversation back up well, or just tells the caller "we got your message."