Visiting Howth With Grandmother

I am visiting Ireland with my grandmother late this upcoming June. I have been twice to Ireland but this is my grandmother's first trip so I want to make it really really special because she's been waiting a while to visit! We always said we'd visit with my grandfather, but every trip plan fell through and he passed away 2 years ago, so making this trip is really meaningful to us.

We are taking the train out to Killarney for a few days and have some time in Dublin, it's kind of weird so how our trains and flights fall we basically have 4 half days (half day when we arrive, half day the second day before our trip to Killarney, half day when we come back from Killarney, half day when we fly out in the afternoon).

I'd really like to take her out to Howth, despite our time in Dublin being limited. The summit viewpoint is just such a special place to me and I really want her to see it. I am thinking about going the morning before we take either the 1pm or 3pm train to Killarney.

The issue is, I'm not entirely sure it's even possible for us to make it happen. It looks like there's a bus that would drop us off right at the summit viewpoint, but I was reading that the bus can get stuck in high traffic at times. I also read that the DART stop is a pretty long uphill walk away, and she cannot walk uphill for that long. She's very fit for being in her 80s, but I don't want to push her too hard! Considering all this, it seems like the odds are just against us to make it happen since we don't even have one continuous day in Dublin.

Does anyone have additional information or experience to talk me in or out of this? Maybe it's still worth going to Howth if we can't get to that particular viewpoint, if there are other worthwhile viewpoints closer to the DART stop? Thanks!