@Melvin this is a pretty common boot fitting issue that we see for customers, and often times we solve it not necessarily by sizing the boots so much bigger, but instead by focusing on securing the foot in place better with insoles. Often when a foot slides forward so much on a downhill that the toes hit the front, there's either too much volume in the boot (this would require a different boot) and/or the arch isn't being held in place properly, causing the foot to flatten and elongate with each step.
While our stores are closed, we do recommend setting up a free virtual outfitting appointment - we'd also recommend starting with a pair of insoles and maybe considering a few specific lacing techniques that can help hold the foot back in the heel cup on the downhill. We'd also be happy to recommend specific boots to consider, although we'll need to know a little more about your wife's feet - are they wide/narrow/medium width? Are they high/low/average volume? Other than her toes, are there any other trouble spots (like bunions)? And what brand is she currently wearing or has worn in the past that has worked for her? Look forward to helping more!