Good advice above. Don't sweat the shipping lanes, at least during daytime and good visibility, there just aren't that many ships. Keep your VHF radio handy in case you want to call on 16 and make sure they see you.
Let the wind guide your route. Got a good brisk summer sou'wester? Then start early and go for it, it's a close reach, about 10 hours at 5 knots, and you have what, about 14-15 hours of daylight? You'll be fine. For a couple of hours you'll be out of sight of land, which is exciting (or boring, or both).
Use your GPS and chart, but you'll see the lighthouse from way off.
Lighter winds or different direction? Consider Scituate, then hop over from there. Might be less boring for your sister. And you have the Boston Monster buoy (used to be the Lightship) and then Minot's light as prominent landmarks to get to Scituate. Don't go as far south as Plymouth, which takes a LONG time to get in and out of.
Then for your return trip, you're both veterans by then, if you get a good persistent summer SW breeze, then definitely one day, a long but easy beam/broad reach.