It sounds like your companion needs to increase their fitness on her bike before they're able to reach the goals that YOU'VE set for yourselves. A lighter frame is only going to do so much in terms of achieving those goals.
Yes, you can throw gravel tires on it (limited to 38c I believe according to the spec's sheet). Is it a smart purchase? I personally would say no, it is not. You know how long it takes YOU to cover certain distances with the equipment you have. Your statistics are not representative of your companion's. You're the stronger rider and therefore, she's always going to have to work harder to keep up with you until she increases her fitness. If her pace is too easy and slow for you, give yourself a challenge and gear up one cog.