It is really hard to say but...............
I have a deerhound who is from coursing lines so he loves nothing more than a chase. He is also bloomin large (in pic with ESS and Brittany).

Now he adores running down my spaniels and he will catch them and pull their feathering etc. The difference being that all the dogs understand the game. He weighs in at 46kg and could do serious damage, lets face it - he is bred to bring down a red deer stag in partnership with a second deerhound.
My spaniels/brittanys all have learned that if they can stop running then Brice loses interest.
So my best advice would be to keep a close eye and if you see the dog on the horizon then call Poppy in. Alternatively you could try doing an Emergency Stop with her and then walking up to her to collect her but if she is scared herself she is likely to run. At the end of the day I would personally rather curtail the walk than have an incident, unfair as that is.
Even if they are traveller types it is also worth letting your Dog Warden know, they may not be prepared to do much but you have registered a concern!