She should first calculate what the rate change will be. Is she going to jump the rates up or creep them up? How far behind is she? Is $5 going to be a big enough raise? Is she thinking more like $25? You can also tell her that if the prices go up she needs to be sure her website reflects ALL the 'freebies' included in that.
Yes, she is 'in competition' for guests but if her product is substantially better and she can prove it, guests will book at the higher price.
Have you stayed at the other place? Worked there? Do you have insider knowledge that your innkeeper's place is better than the other place?
There is no need to announce rate changes, just do it. Her rates for tomorrow could be higher than today's and who's to know? She needs to honor any reservations made at the old price. We never announce changes, just make sure all the web marketing reflects the changes. Make a list of all the directories she's on and be sure all of those ranges get changed. Ditto her own website.
Now, if the question is really, 'How do I tell the long-time repeats the price has gone up,' that's something else altogether. Most of them have gotten used to the old pricing. If they really like the place they'll understand a raise in the price and there is no need to warn them in advance. If it is a big jump and the guests have been coming forever, she could do a tiered pricing just for them (unannounced). She could jump them half this year and half next.
If she is hearing comments that imply she is not charging enough then it's time!