She can use the option of teleporting or swimming.

The only suggestions that spring to mind are: 1. Wait and hope that a tunnel or bridge is built between the UK and Ireland - there have been proposals in the past and it is probably technically (if not economically) feasible. 2. Wait until the next ice age when the sea will probably freeze and you will be able to walk across. 3. Try to cure your sister's fear of planes and/or boats. Some airlines offer courses that can help.

Since there are no tunnels or bridges to Ireland, I'd be tempted to just say 'no', but did you have anything in mind yourself (swimming? Hiking the seabed? A balloon?)

Does she count a hovercraft as a boat? Or are you using boat as shorthand for surface vessel?

@MadHatter If you're frightened of planes and boats, surely you'll love a form of transportation that will leave you wondering whether you're seasick or airsick :)

Voting to migrate this to puzzling.SE

You can go to North Ireland. Then with car or buses, you can go to Ireland (as the Republic of Ireland).

@GiacomoCatenazzi The question is not about the Republic of Ireland but explicitly about the island named Ireland. So, Northern (not North) Ireland is already included in the question and is not a separate option.

Perhaps your sister actually doesn't want to go to Ireland, and is reluctant to say so.

Wait for Musk to finish his rocket plans. But I guess that one carries a (very reasonable) fear with it, too.

You could try the Pirates of the Carribean trick of holding a dinghy upside-down and walking along the seafloor.

Maybe a submarine

@anomuse Careful with terminology! The UK includes Northern Ireland which is connected by land to Ireland (the country). You probably meant Great Britain.

“Ireland is an island” is the best answer.

Would you count an amphibious car as a ‘boat’?

Just fly there with Qantas :)

Would having her willingly come to the port in Holyhead, clear immigration and then fall asleep or unconscious (some medicine or heavy drinking, her choice) and next thing she notices when she wakes up (2 or more hours later) is beautiful Ireland below her feet, count as not sailing or flying, since she did not experience that?

I assume that starting in Northern Ireland is out of the question?

My mother swears by getting really drunk at the port-side bar, then spending the entire journey unconscious, then getting poured into a car at the other side, debarking and waking up at the hotel.

I'm surprised nobody has made any jokes about parasailing, or suggested windboarding/kiteboarding.