Well I had a similar experience w/my boxer (who was 9) when I introduced my older bulldog Walter. It took some time, but she finally got used to the idea of him hanging around… Lol Make sure to give her time during the day to get a "puppy" break… I would put Walter in the crate to let Roxie get some rest. And at night she slept in our bedroom, while Walter was in his crate in our bathroom. I would make sure to do things w/them together like training, taking walks, or playing fetch. I think that Walter gave Roxie some excitement in her later years, although she would be exhausted by the end of the day. Turn around is fair play, because after my beloved Roxie passed we NOW have Willow who is 8 mos of bulldog puppy madness. Walter is getting a fair dose of his share these days… Lol Give it time, but be prepared… they may not be "best" buddies, but IMO single dogs get very lonely and it's always better to spend your day w/a buddy.