77.8 IV Lapras with IS/IB

It is, but only when you have the candies to power it up to where it will be usable for you. For some players that might be level 30, for others it might only be 25, for example.

You don't want to power it up as you go along in case you end up getting a higher levelled Lapras which needs less power ups, because then you'll have wasted your candies on this Lapras if it's not at a high enough CP to be usable.

I'm in a similar situation to you, mines level 10, 801 CP with IS/B. Walk it as a buddy for now, and use the CP calculator (here: https://pokemongo.gamepress.gg/cpcalc#/)to figure out where you want to power it up to, and how many candies you'll need to get to that stage.

Once you have enough, power it up. The difference that a Lapras with better IVs will have is hardly noticable, and it also needs to have the same moveset in order to be better, since yours has the best defending moveset, and the odds of this happening are insanely low that it's not worth waiting for such a small increase in effectiveness.

inb4 "wait for one with better IVs"

You can hatch another one tomorrow, or it it can take months to get another one. I dont count the chances to get a bad moveset or low IVs. Imo the best thing to do is calculate the amount of candies she needs at least to lvl 30 (I consider that you dont have much candies since this is your first Lapras) and start to collect with walking your Lapras asap. Do not do any power ups until you get the required candies. In the duration you have the chance to hatch or caught a better one and if that happens you will have your resources ready.

I would advise everyone to remember from which Poke stop you get your 10 km eggs, in case you hatch a Lapras. Although some guys here believe that it's not true, but the chances that the same Pokestop gives you a Lapras again are higher than anything else you could try. I got my two Lapras on November, 25th, and December 14th, from the very same Pokestop. Yes, the sample size is small, but still I'm convinced that this is not a coincidence. I noticed the same thing with Chansey and Porygon also.